Symfony2 create new entity error: NotFoundException

I am getting NotFoundHttpException error when I try to create new entity with form.

This is a code for creating form and entity - CategoryController:

 /**
 * Displays a form to create a new Category entity.
 *
 * @Route("/new", name="category_new")
 * @Method({"GET"})
 */
public function newAction(Request $request)
{
    $entity = new Category();
    $form   = $this->createCreateForm($entity);


    return array(
        'entity' => $entity,
        'form'   => $form->createView(),
    );
}

/**
 * Creates a new Category entity.
 *
 * @Route("/", name="category_create")
 * @Method("POST")
 * @Template("AdminBundle:CategoryPanel:new.html.twig")
 */
public function createAction(Request $request)
{
    $entity = new Category();
    $form = $this->createCreateForm($entity);
    $form->handleRequest($request);

    if ($form->isValid()) {
        $em = $this->getDoctrine()->getManager();

        $em->persist($entity);
        $em->flush();

        return $this->redirect($this->generateUrl('category_show', array('id' => $entity->getId())));
    }

    return array(
        'entity' => $entity,
        'form'   => $form->createView(),
    );
}

/**
 * Creates a form to create a Category entity.
 *
 * @param Category $entity
 *
 * @return \Symfony\Component\Form\Form The form
 */
private function createCreateForm(Category $entity, ServiceCategory $parentCategory = null)
{
    $form = $this->createForm(CategoryType::class, $entity, array(
        'action' => $this->generateUrl('category_create'),
        'method' => 'POST',
        'parentCategory' => $parentCategory
    ));

    $form->add('submit', SubmitType::class, array(
        'label' => 'Create',
        'attr' => array(
            'class' => "btn btn-primary"
        )
    ));

    return $form;
}

CategoryType

      public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder->add('name', TextType::class, array('label' => 'Category name'));

    $parentCategory = $options["parentCategory"];

    if($parentCategory != null){
        $builder->add('parent', 'entity', array(
            'class' => "CoreBundle:ServiceCategory",
            'choices' => array($parentCategory)
        ));
    }else{
        $builder->add('parent', 'entity', array(
            'class' => "CoreBundle:ServiceCategory",
            'query_builder' => function(ServiceCategoryRepository $cp){
                $qb = $cp->createQueryBuilder('c');
                return $qb;
            },
        ));
    }

}

Why this code is looking for entity when I am only attempting to create it?

UPDATE

new.html.twig

{% extends 'AdminBundle:AdminPanel:base.html.twig' %}

{% block body -%}
<h1>Category creation</h1>

{{ form_start(form) }}
{{ form_row(form.name) }}
{{ form_row(form.parent) }}

<ul class="record_actions">
    <li style="display: inline-block">
        {{ form_widget(form.submit) }}
    </li>
    <li style="display: inline-block">
        <a href="{{ path('category_panel_index') }}">
            <button type="button" class="btn btn-primary">
                Back to the list
            </button>
        </a>
    </li>
</ul>
{{ form_end(form) }}

{% endblock %}